In my opinions the primary unique selling point of Captain of Industry is the mining/destructable landscape. This brings the excitement of being able to imagine how things might be, but also with it the expectation. Therefore players don't want to just make a living industrial machine, they want to make something that looks like a living industrial machine.
To that end my suggestion is that the mechanics are able to change the way the game looks to match the creative ambitions of players. Starting with roads, which are intended to be incorporated and something like asphalt which has previously been suggested, I specifically suggest the following as a starting point for discussion:
Individual housing (while keeping the excellent housing facilities mechanic)
Road options (concrete/asphalt)
Extra buildable levels (probably not very easy but would be absolutely amazing)
I want to be able to build a multi-layer factory on a hill looking down on the docking and housing area!